1. Technical Field
This invention is a control for automatically adjusting the position of a support for a milker unit when a cow is milked.
2. Background Art
A milker unit draws milk from a cow's teats and is connected to a carry-away pipeline. Milk flow during milking is improved by applying the weight of a milker unit to a cow's teats to produce a positive or "live" action tug and pull on the teats. Apparatus for positioning a milker unit below a cow and providing a tug and pull effect is shown in Thomas U.S. Pat. Nos. 2,747,544, 3,605,694 and 3,605,695 and in Babson U.S. Pat. Nos. 2,613,636 and 3,033,161, all of which are assigned to the assignee of this application. The apparatus described in the above-identified patents hold a milker unit at a preset position below a cow during milking unless an operator adjusts the milker unit height.
Increasing slackness (or decreasing tautness) in a cow's udder during milking causes the height of a milker unit for achieving optimum tug and pull to change during the milking process. Specifically, a milker unit typically is connected to a support with a flexible member, such as a chain. Sag in a cow's teats during milking can cause the milker unit to lower so that the chain becomes taut and the weight of the milker unit is carried by the support rather than the cow's teats. A problem with prior apparatus in which a milker unit is held at a preset position is that the apparatus do not take into account the change in milker unit height required to apply continuously the weight of the milker unit to the cow's teats.
A support for automatically changing the position of a milker unit during milking is shown in commonly assigned Needham et al U.S. Pat. No. 3,999,518, issued Dec. 28, 1976. The Needham milker support has an electronic control for incrementally lowering a milker unit at equal time intervals during milking. A problem with the milker support described by Needham is that because the milker unit lowers at fixed time intervals and not as a direct function of force applied to the support, it is possible for at least a portion of the weight of the milker unit to be relieved from a cow's teats. For example, if the rate at which a cow's teats slacken exceeds the rate at which the control lowers the milker unit, the chain can become taut so that the weight of the milker unit is carried by the support. The chain also can become taut and the support similarly will carry the weight of the milker unit if the rate at which a cow's teats slacken is less than the rate at which the control lowers the milker unit.